Looks like you've got light leaking into your res bro. Are you roots slimy ? I'm guessing yes. You need to go out and get some panda film or one of those relective tings you sit in the dash of your car to keep heat out. Then, cut it to fit around your res and rap it. Then, cut a piece big enough to cover the top, cut a slit halfway through it down the middle, and slide it on the top.
With light leaking in it also gets hotter in there and both things are promoting root rot. Your going to have to cut your roots off at the bottom of your pot and change out your res solution. Then, take about a teaspoon of rooting hormone (you can get it at most garden places, even home cheapo) and desolve it into a half litre of water, Then, pour that into your net pot and let it soak into your roots.
I had to do this a week or so into flowering and it only took about a week and a half for my roots to come back stronger than before I cut them.
Good luck man!